1. Field of the Invention
The present invention relates to system for laying a subterranean water impervious asphalt layer which is mounted on a tractor and includes a liquidized asphalt supply tank, a liquidized asphalt supply pipe and outlet ports for discharging liquidized asphalt, and more particularly, to a system for strewing liquidized asphalt by the tractor referred to the above as well as for removing liquidized asphalt from the liquidized asphalt supply pipe and the outlet ports after the operation of the tractor.
2. Description of the Prior Art
A system for laying a subterranean water impervious asphalt layer has been recently developed, for example, as shown in U.S. Pat. No. 3,276,208 in order to render a tract of barren land such as a desert to be useful as a farming area or a tree planting area. The subterranean water impervious asphalt layer serves to prevent water on the surface of the earth from permeating into the depth of earth as well as to prevent water containing much salt from rising to the surface of the earth.
Prior art system for laying the subterranean water impervious asphalt layer suffers from difficulties such as inconvenience in controlling various valve means for properly operating the tank and troubles in sticking asphalt in the piping and the outlet ports in the tractor after the operation of the tractor is terminated which makes it very troublesome to quickly commence the next operation of the tractor.
The present invention aims at avoiding the difficulties occurring in the prior art system for laying a subterranean water impervious asphalt layer as referred to the above.